Titanium dioxide film co-doped with yttrium and erbium and method for procucing the same

ABSTRACT

A doped TiO 2  material for forming a film used in a planar optical waveguide amplifier. The doped TiO 2  material includes 100 mol % TiO 2  precursor compound, 0.1˜10 mol % erbium ion (Er 3+ ) precursor compound, and 1˜50 mol % yttrium ion (Y 3+ ) precursor compound, thereby forming the doped TiO 2  film co-doped with erbium and yttrium as an amorphous structure to achieve the enhancing effect on photoluminescence properties.

FIELD OF THE INVENTION

[0001] The present invention relates to a TiO₂ film co-doped withyttrium and erbium and a method for producing the yttrium and erbiumco-doped TiO₂ film, and more particularly to an yttrium and erbiumco-doped TiO₂ film used in a planar optical waveguide amplifier.

BACKGROUND OF THE INVENTION

[0002] Owing to the development of network communication, the loading ofthe network information transference is heavier and heavier. Forincreasing the data capacity carried by the transform system, theoptical fiber system is applied in the communication system forsatisfying the demand.

[0003] The most important elements of the optical communication systemare light source and optical-guided medium. Owing to the disclosure ofthe semiconductor laser, the long effect and stable light source can bepractically applied. At the same time, the quartz optical fiber havinglow transmission loss has been developed. However, during optical fibertransmission, the transmission loss is inevitable. Thus, it is necessaryto set an amplifier at the intermediate station for a long distancetransmission. Traditionally, the amplifier is used to transfer anoptical signal to an electrical signal, amplify the electrical signal,transfer the amplified electrical signal to the amplified opticalsignal, and transmit out the amplified optical signal. After thedisclosure of the erbium-doped fiber amplifier (EDFA), however, theoptical signal can be directly amplified and transmitted out.

[0004] During the light transmission, the light source having awavelength of 1.53 μm has lower loss and is harmless for human eyes.When erbium ion is excited by the laser with the wavelength of 1.48 μm,0.98 μm or 0.8 μm, the electron located on the first exciting state willjump back to the ground state and irradiate an infrared ray withwavelength of 1.53 μm. The infrared spectra are the light source appliedin the current optical fiber communication.

[0005] Currently, along the development and upgrade of the ICsemiconductor producing technology, the microphoto-electromechanicsystem is quickly developed. For the integrated optics devices, theplanar optical amplifier has very important applications. Furthermore,because the size of the planar optical amplifier is much smaller thanthat of the erbium-doped fiber amplifier, the erbium-doped planaroptical waveguide amplifier becomes an important issue in the integratedoptics. Referring to the erbium-doped planar optical waveguideamplifier, most researches are focus on either the process improvementor the different host selection. Generally, the major material of thehost is oxide glass, such as pure silica, soda-lime silicate,phosposilicate and aluminosilicate glass, because the oxide glass is themajor material for current optical fibers. However, the ceramicsmaterial such as Al₂O₃, TiO₂, Y₂O₃ and LiNbO₄, or the amorphous siliconmaterial are also used to be the host. The shape and intensity oferbium-ion fluorescence spectrum are affected by different host.Furthermore, the fluorescence spectral characteristics are dependent onthe solubility, or the radiative /non-radiactive relaxation of theerbium ion in the host.

[0006] The cross-relaxation between erbium ions will decrease the numberof excited erbium ion. The cross-relaxation strength between erbium ionsis dependent on the distance between the erbium ions. That is, while theclustering effect of erbium ions increases, the photoluminescenceefficiency decreases. In addition, a hydroxide group is aphotoluminescence quenching center because the second harmonic vibrationof the hydroxide group can produce resonant effect with the ˜1.54 μmphotoluminescence of erbium ion, which results in the photoluminescenceefficiency decreasing. Moreover, the up-conversion phenomenon caused bythe cross-relaxation effect between erbium ions will also decrease thephotoluminescence efficiency. Therefore, the photoluminescenceefficiency can be improved by increasing the erbium ion solubility inhost, decreasing the hydroxide group content in host, or decreasing theprobability of the up-conversion, and more especially by increasing theerbium ion solubility in host. Generally, the aluminum ion is doped intothe silicon oxide structure for increasing the erbium ion solubilitybecause the aluminum ion can be a network former and a network modifierto break the tetrahedron network structure of silicon oxide. Thus, thenumber of non-bridging oxygen is increased, which further increases theerbium ion solubility.

[0007] Another way to increase photoluminescence efficiency is basicallyto change host materials because the erbium ion solubility in host isstrongly host-dependent. Thus, a proper host can increase the erbium ionsolubility and further increase the photoluminescence efficiency. SinceTiO₂ host has higher refraction index (n=2.52 for anatase and n=2.76 forrutile), the optical modes are increased for enhancing transmissionefficiency and decreasing the bending radii of the optical waveguide.Hence, the size of optical waveguide device is largely decreased. Inaddition, TiO₂ host also has lower phonon energy (<700 cm⁻¹), so theexcited electrons are decreased by non-radiative losing rate.

[0008] Therefore, Er³⁺-doped TiO₂-based film is applied in the planaroptical waveguide amplifier. However, the photoluminescence propertiesof Er³⁺-doped TiO₂ film applied in the planar optical waveguideamplifier are not as good as expectation.

[0009] Therefore, the purpose of the present invention is to develop amaterial and a method to deal with the above situations encountered inthe prior art.

SUMMARY OF THE INVENTION

[0010] It is therefore an object of the present invention to propose anerbium and yttrium co-doped TiO₂ material and a method for producing theerbium and yttrium co-doped TiO₂ film used in a planar optical waveguideamplifier for increasing ˜1.54 μm photoluminescence in emissiveintensity.

[0011] It is therefore another object of the present invention topropose an erbium and yttrium co-doped TiO₂ material and a method forproducing the erbium and yttrium co-doped TiO₂ film used in a planaroptical waveguide amplifier for increasing ˜1.54 μm photoluminescence inbandwidth.

[0012] It is therefore an additional object of the present invention topropose an erbium and yttrium co-doped TiO₂ material and a method forproducing the erbium and yttrium co-doped TiO₂ film used in a planaroptical waveguide amplifier for decreasing light scattering.

[0013] It is therefore an additional object of the present invention topropose an erbium and yttrium co-doped TiO₂ material and a method forproducing the erbium and yttrium co-doped TiO₂ film used in a planaroptical waveguide amplifier for decreasing processing temperature andfurther reducing the producing cost.

[0014] According to one aspect of the present invention, there isprovided a doped TiO₂ material for forming a film used in a planaroptical waveguide amplifier. The doped TiO₂ material includes 100 mol %TiO₂ precursor compound, 0.1˜10 mol % erbium ion (Er³⁺) precursorcompound, and 1˜50 mol % yttrium ion (Y³⁺) precursor compound, therebyforming the doped TiO₂ film co-doped with erbium and yttrium as anamorphous structure to achieve the enhancing effect on photoluminescenceproperties.

[0015] Preferably, the erbium ion (Er³⁺) precursor compound is selectedfrom a group consisting of erbium acetate, erbium carbonate, erbiumchloride, erbium oxalate, erbium nitrate, and erbium isopropoxide.

[0016] Preferably, the TiO₂ precursor compound is selected from a groupconsisting of titanium isopropoxide, titanium ethoxide, titaniumchloride, and titanium butoxide.

[0017] Preferably, the yttrium ion (Y³⁺) precursor compound is selectedfrom a group consisting of yttrium acetate, yttrium carbonate, yttriumchloride, yttrium oxalate, yttrium nitrate, and yttrium isopropoxide.

[0018] According to another aspect of the present invention, there isprovided a method for forming a doped TiO₂ film used in a planar opticalwaveguide amplifier. The method includes steps of (a) preparing atitanium solution having 100 mol % titanium ion (Ti⁴⁺) precursorcompound, (b) preparing a yttrium solution having 1˜50 mol % yttrium ion(Er³⁺) precursor compound, (c) adding the yttrium solution and an erbiumpowder with 0.1˜20 mol % into the titanium solution for forming asol-gel solution and (d) forming the TiO₂ film co-doped with Er³⁺ andY³⁺ by spin-coating and thermal treatment.

[0019] Certainly, the step (a) can further include steps of (a1)dissolving titanium isopropoxide in acetic acid to from a first solutionand (a2) adding 2-methoxyethanol into the first solution.

[0020] Certainly, the step (b) can further include step of dissolvingyttrium acetate in a mixed solution of methanol and ethylene glycol.

[0021] Preferably, the step (d) further includes steps of (d1)spin-coating the sol-gel solution on a substrate, (d2) thermal treatingthe substrate at a first specific temperature for evaporating organicmaterials thereof, (d3) repeating steps of spin-coating and thermaltreating until the film reaching a specific thickness and (d4) thermaltreating the film of the substrate at a second specific temperature forforming the TiO₂ film co-doped with Er³⁺ and Y³⁺.

[0022] Certainly, the substrate can be made of a material selected froma group consisting quartz, glass, and silica oxide on silicon (SOS).

[0023] Preferably, the first specific temperature is about 400° C. andthe second specific temperature is ranged from 500 to 900° C.

[0024] Preferably, the specific thickness of the film is ranged from 0.1to 2 μm.

[0025] The present invention may best be understood through thefollowing description with reference to the accompanying drawings, inwhich:

BRIEF DESCRIPTION OF THE DRAWINGS

[0026]FIG. 1 is a plot illustrating X-ray diffraction patterns ofdifferent ratio Er₂O₃: Y₂O₃ : TiO₂ films treated at differenttemperature for 1 hour, wherein A, R, and P represent anatase, rutile,and pyrochlore phase respectively;

[0027]FIG. 2 is a plot illustrating chromatic dispersion curve ofdifferent ratio Er₂O₃: Y₂O₃: TiO₂ films treated at 700° C. for 1 houraccording to the present invention;

[0028]FIG. 3 is a plot illustrating ˜1.54 μm fluorescence spectra ofdifferent ratio Er₂O₃: Y₂O₃: TiO₂ films treated at 700° C. for 1 houraccording to the present invention;

[0029]FIG. 4 is a plot illustrating ˜1.54 μm photoluminescenceintensities of the erbium and yttrium co-doped TiO₂ film treated at 700°C. for 1 hour with different Er₃₊ and Y³⁺ concentrations according tothe present invention;

[0030]FIG. 5 is a plot illustrating ˜1.54 μm fluorescence spectra of theerbium and yttrium co-doped TiO₂ film treated at 700° C. for 1 hour andthe best ratio of erbium and aluminum co-doped TiO₂ film with the bestmolar ratio and treated at 700° C. for 1 hour according to the presentinvention; and

[0031]FIG. 6 is a plot illustrating ˜1.54 μm fluorescence spectra of theerbium and yttrium co-doped TiO₂ film treated at different temperatureranged from 700 to 900° C. for 1 hour according to the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0032] The present invention discloses a TiO₂ host co-doped with erbiumand yttrium to form a TiO₂ film. Owing to the presence of yttrium ion,the erbium and yttrium co-doped TiO₂ film has 10 times ˜1.54 μmphotoluminescence intense emission and 1.5 times bandwidth offluorescence spectrum than the erbium and aluminum co-doped TiO₂ filmhas, which is thought a material having excellent photoluminescenceproperty. In addition, the erbium and yttrium co-doped TiO₂ filmrequires lower processing temperature and lower producing cost, so it isa potential material used in the planar optical waveguide amplifier ofthe integrated optics.

[0033] The preparation of the erbium and yttrium co-doped TiO₂ filmmaterial is performed by the sol-gel spin coating process. First, a Er³⁺precursor such as erbium acetate and a Y³⁺ precursor such as yttriumacetate are added into a Ti⁴⁺ precursor such as titanium isopropoxide toform a clear solution, wherein the ratio of Er³⁺: Y³⁺: Ti⁴⁺ isrepresented as X: Y: 1 (mol). Subsequently, the clear solution isapplied with spin coating and thermal treatment to obtain a TiO₂amorphous structure co-doped with high concentrations of erbium andyttrium.

[0034] Referring to the preparation of the sol-gel solution, first,titanium isopropoxide is dissolved into an acetate solution. Afterstirring, 0 2-methoxyethanol is added and is agitated violently. On theother hand, yttrium acetate is added into a methanol/ethylene glycolsolution with a molar ratio of 3:1. A certain ratio erbium acetatepowder and the above yttrium acetate solution are added into thetitanium isopropoxide solution together. Then, the mixture solution isagitated for at least 10 hours in order to process homogenous hydrolysisand condensation reaction among titanium, erbium and yttrium ions.

[0035] Regarding to the preparation of the film, first of all, thesol-gel solution is homogenously sputtered on a fused quartz substrateand spin-coated at a speed of 4000 rprn/30 sec. After coating, eachlayer of the film is dried at 150° C. on a hot plate for evaporating thesolvent. Then, the film is treated at 400° C. for 30 minutes at aheating rate of 5° C. /min to remove the remained organic material ofthe film. The spin-coating and annealing steps are repeated until the0.5 μm thickness of film is deposited. Then, the film is treated at thetemperature ranged from 600 to 1000° C. for 1 hour at a heating rate of10° C./min. Table 1 shows the full width at half maximum (FWHM) ofphotoluminescence of film samples at ˜1.54 μm with different molar ratioof erbium/yttrium/titanium and erbium/aluminum/silicon, wherein theEr:Al:Si ratio of samples E and F are formed the best compositionshaving the most intense photoluminescence according to Y Zhou's paperpublished in Applied Physical Letters, vol.71, p587-589 at 1997.Table 1. The FWHM of photoluminescence in film samples at ˜1.54 μm ofdifferent ratio erbium/yttrium/titanium and erbium/aluminum/ silicon.Sample A B C D E F Er:Y:Ti 5:0:100 5:10:100 5:30:100 10:30:100 — — (mol%) Er:Al:Si — — — — 0.7:0:100 0.7:8:100 (mol %) FWHM 13 36 75 75 27 50of PL at ˜1.54 μm (nm)

[0036]FIG. 1 is a plot illustrating X-ray diffraction (XRD) patterns ofdifferent ratio Er₂O₃: Y₂O₃: TiO₂ films treated at different temperaturefor 1 hour, wherein A, R, and P represent anatase, rutile, andpyrochlore phase respectively. As a pure TiO₂ film (Er₂O₃: Y₂O₃:TiO₂=0:0:100) is annealed at 700° C., an anatase phase 101 is observed.However, with the incorporation of 5 mol % Er³⁺ and 10 mol % Y³⁺ intoTiO₂ network, the XRD peak of TiO₂ phase was broadened, indicating thecrystallinity of matrix host becomes poor. Furthermore, as increasingthe doping concentration of Y³⁺ to 30 mol %, a weak broad continuum inthe XRD was observed, which is characteristic of amorphous structure.Thus, while Er³⁺ or Y³⁺ are added into TiO₂ network, the crystallinityof TiO₂ (i.e. anatase phase) will significantly decrease. While theannealing temperature is 800° C. and the ratio of Er₂O₃: Y₂O₃: TiO₂ is5:30:100, a strong preferred peak 222 is observed, demonstrating apyrochlore phase with the formula of Er_(x)Y_(2-x)Ti₂O₇ is developed inthe TiO₂-based amorphous structure. While the annealing temperature is1000° C., another weak peak 110 is observed, demonstrating a rutilephase is developed in the TiO₂-based amorphous structure.

[0037]FIG. 2 is a plot illustrating chromatic dispersion curve ofdifferent ratio Er₂O₃: Y₂O₃: TiO₂ films treated at 700° C. for 1 houraccording to the present invention. As shown in FIG. 2, a pure TiO₂ film(Er₂O₃: Y₂O₃: TiO₂=0:0:100) is annealed at 700° C. for 1 hour, therefractive index of the TiO₂ film is 2.28. While the TiO₂ film isco-doped with 5 mol % Er³⁺ and 10 mol % or 30 mol % Y³⁺, the refractiveindexes decrease from 2.28 to 2.25 and from 2.28 to 2.13. Thus,according to the change of Y³⁺ concentration, the preparation of an Er³⁺and Y³⁺ co-doped TiO₂ film with flexible refractive index can beachieved.

[0038] As show in FIG. 3, while the Er³⁺ doping concentration is 5 mol%, once the addition of Y³⁺ concentration reaches above 20 mol %, theintensity increases 3˜4 times and the bandwidth increases from 35 nm to75 nm at the ˜1.54 μm photoluminescence intensity.

[0039] As shown in FIG. 4, the more Y³⁺ is doped into the host, thestronger the ˜1.54 μm photoluminescence intensity is, even though theEr³⁺ doping concentrations are different in the host (1, 5, and 10 mol%). In addition, FIG. 5 shows that the Er³⁺ and Y³⁺ co-doped TiO₂ filmaccording to a preferred sample of the present invention has 10 timesfor photoluminescence intensity and 1.5 times for bandwidth than of theEr³⁺ and Al³⁺ co-doped silica film with an optical molar ratio of0.7:8:100 has. Therefore, the photoluminescence properties of the Er³⁺and Y³⁺ co-doped TiO₂ film has more intense emission and wider bandwidthwhile comparing with that of the pure TiO₂ film or that of the Er³⁺ andAl³⁺ co-doped silica film.

[0040]FIG. 6 illustrates the photoluminescence intensity of the Er³⁺ andY³⁺ co-doped TiO₂ film treated at the different annealing temperatures.The result shows the intensity of Er³⁺ and Y³⁺ co-doped TiO₂ filmincreases with the increasing temperature when the temperature is notmore than 700° C. However, the spectrum of Er³⁺ and Y³⁺ co-doped TiO₂film is not significantly changed at this condition. Once the annealingtemperature increases to or over 800° C., the photoluminescenceintensity decreases and the spectrum is divided into several small peaksas shown in FIG. 6.

[0041] The present invention provides an Er³⁺ and Y³⁺ co-doped TiO₂ filmand a method for producing the same. The TiO₂ film co-doped with 5 mol %Er³⁺ and more than 30 mol % Y³⁺ and annealed at 700° C. has the bestphotoluminescence properties when the Er³⁺ and Y³⁺ co-doped TiO₂ film isapplied in the planar optical waveguide amplifier. Therefore, thepresent invention has the following advantages:

[0042] (1) The Er³⁺ and Y³⁺ co-doped TiO₂ film has 4 times forphotoluminescence intensity at ˜1.54 μm and 2 times for bandwidth thanthe Er³⁺ doped TiO₂ film has.

[0043] (2) When comparing with a typical Er³⁺ and Al³⁺ co-doped silicafilm used in the planar optical waveguide amplifier, the Er³⁺ and Y³⁺co-doped TiO₂ film has 10 times for photoluminescence intensity at ˜1.54μm, 1.5 times for bandwidth, and 1.3 times for refraction.

[0044] Therefore, an amplifier device produced by the Er³⁺ and Y³⁺co-doped TiO₂ film has higher efficiency and smaller size.

[0045] (3) The Er³⁺ and Y³⁺ co-doped TiO₂ film has an amorphousstructure, so the light scattering can be decreased.

[0046] (4) The temperature of thermal treatment is about 700° C. that ismuch lower than the typical processing temperature for the Er³⁺ and Al³⁺co-doped silica film, so the present invention can decrease largely theprocessing temperature and further reduce the producing cost. Inaddition, the lower temperature is more properly applied in the planaroptical waveguide amplifier because the typical quartz substrate cannotendure higher temperature in the process.

[0047] While the invention has been described in terms of what arepresently considered to be the most practical and preferred embodiments,it is to be understood that the invention need not to be limited to thedisclosed embodiment. On the contrary, it is intended to cover variousmodifications and similar arrangements included within the spirit andscope of the appended claims which are to be accorded with the broadestinterpretation so as to encompass all such modifications and similarstructures.

What is claimed is:
 1. A doped TiO₂ material for forming a film used ina planar optical waveguide amplifier, comprising: 100 mol % TiO₂precursor compound; 0.1˜10 mol % erbium ion (Er³⁺) precursor compound;and 1˜50 mol % yttrium ion (Y³⁺) precursor compound; thereby formingsaid doped TiO₂ film co-doped with erbium and yttrium as an amorphousstructure to achieve the enhancing effect on photoluminescenceproperties.
 2. The doped TiO₂ material according to claim 1, whereinsaid erbium ion (Er³⁺) precursor compound is selected from a groupconsisting of erbium acetate, erbium carbonate, erbium chloride, erbiumoxalate, erbium nitrate, and erbium isopropoxide.
 3. The doped TiO₂material according to claim 1, wherein said TiO₂ precursor compound isselected from a group consisting of titanium isopropoxide, titaniumethoxide, titanium chloride, and titanium butoxide.
 4. The doped TiO₂material according to claim 1, wherein said yttrium ion (Y³⁺) precursorcompound is selected from a group consisting of yttrium acetate, yttriumcarbonate, yttrium chloride, yttrium oxalate, yttrium nitrate, andyttrium isopropoxide.
 5. A method for forming a doped TiO₂ film used ina planar optical waveguide amplifier, comprising steps of: (a) preparinga titanium solution having 100 mol % titanium ion (Ti⁴⁺) precursorcompound; (b) preparing a yttrium solution having 1˜50 mol % yttrium ion(Er³⁺) precursor compound; (c) adding said yttrium solution and anerbium powder with 0.1˜20 mol % into said titanium solution for forminga sol-gel solution; and (d) forming said TiO₂ film co-doped with Er³⁺and Y³⁺ by spin-coating and thermal treatment.
 6. The method accordingto claim 5, wherein said step (a) further comprising steps of: (a1)dissolving titanium isopropoxide in acetic acid to from a firstsolution; and (a2) adding 2-methoxyethanol into said first solution. 7.The method according to claim 5, wherein said step (b) furthercomprising step of dissolving yttrium acetate in a mixed solution ofmethanol and ethylene glycol.
 8. The method according to claim 5,wherein said step (d) further comprising steps of: (d1) spin-coatingsaid sol-gel solution on a substrate; (d2) thermal treating saidsubstrate at a first specific temperature for evaporating organicmaterials thereof; (d3) repeating steps of spin-coating and thermaltreating until said film reaching a specific thickness; and (d4) thermaltreating said film of said substrate at a second specific temperaturefor forming said TiO₂ film co-doped with Er³⁺ and Y³⁺.
 9. The methodaccording to claim 8, wherein said substrate is made of a materialselected from a group consisting quartz, glass, and silica oxide onsilicon (SOS).
 10. The method according to claim 8, wherein said firstspecific temperature is about 400° C.
 11. The method according to claim8, wherein said second specific temperature is ranged from 500 to 900°C.
 12. The method according to claim 8, wherein said specific thicknessof said film is ranged from 0.1 to 2 μm.